Colors

³¹ Colors are remarkably illustrated by the experiment of the Prism, and the real assertions of the blind man left to posterity by that man of greatest diligence, Robert Boyle[cite: 1].

He said that he perceived by touch the very rough surface of white and black, and the very smooth surface of red (although sometimes a varying blue was presented).

He perceived black to be rougher than white, and that other colors, as they depart from the extremes, seem to decrease in roughness.

If this is so, I would believe that white is more [conducive] to light to turn the convexity towards the blackness, the concavity away from it; whence the former reflects light, the latter hides it; and the black surface will have less smoothness, but more roughness.

Firing also produces redness, because it smooths away the inequalities. But these remarks are incidental; for our purpose here is to reduce motions rather than qualities to their principles.

That darkness has no proper effluvium, but appears only as a distance or gap between the parts of the sensory organ affected by light, you may conclude from this: that darkness is not gathered by any mirrors or lenses.

Add this: where there is much aqueous humor, there is much blackness, because that humor is entirely alkaline or empty (of which below), therefore transparent, therefore admitting light, not reflecting it; add also that colors in most cases arise not only from reflection, but also from a certain subtle light or inherent fire mixed in, dispersed with no less perpetuity than the effluvia of odors, although rarely in darkness without another light moving the eyes, yet perhaps sometimes capable of being varied.

³² Sound does not consist in the motion of the air. For I call “air” that thing whose gravity is felt in the Baroscope, which can be compressed, exhausted, and weighed.

When vessels are exhausted and closed in any way, a bell struck inside can be heard from the outside.

Sound consists, therefore, in the motion of the aether. But it is a moderate motion that goes out in circles, as we see when a stone is cast into water.

Whereas light consists in a strong and straight motion of a more subtle part.

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But odor consists in air.

Air is subtle water. By its flow, it dissolves the subtle parts of salts no less than thick water dissolves thick ones.

Just as, therefore, we perceive saltiness in water by taste, so we perceive subtle salts dissolved in the air by smell: so that the nostrils are as it were the place where we “taste” the air.

By “salt,” however—lest there be a question about the word in this place (for below “voice” is used in a far different sense)—I mean with Geber whatever is soluble in any liquor.

³³ Reactions are central to solutions of this kind.

For a central solution occurs by the opening of central bubbles, whence comes the action and transformation of which we shall speak soon; a superficial solution, on the contrary, occurs only by the opening of the surfaces of the bubbles, by a central disintegration, which happens in reality by liquid parts proportioned to themselves creeping into the pores.

Whence soon, when another dissimilar [part] supervenes, precipitation occurs[cite: 1].

Superficial bubbles, however, are formed only by a thick, sensible, and external fusion, but a weak one, whence dissolved metals can be reduced into a body by fire; central ones are formed by a certain insensible and internal fusion, and—as long as we have not found the key nor shaken out the secrets of nature—they are formed by a slow but firm fusion; although nature often produces similar species in an instant.

³⁴ The cause of heat is the same as that of light, differing only in subtlety.

Both arise from internal motion returning upon itself, projecting the subtler parts of itself (see above, §7), and produce heat.

Whence also silence and the aggregation of homogeneous substances. On the other hand, cold, which constricts, arises from a certain strong and rectilinear but coarse motion, which is blunting, not penetrating, and therefore not dissolving but constricting.

Moreover, hard things, or things otherwise dense and compact, are for the most part cold, such as marble, metal, mercury, because their pores are narrow, through which air or wind passes. Whence wind, causing cold, is constricted and gathered together, just as in cities narrow alleys are accustomed to have the most cold.

I add one thing for greater clarity: the impressions of hot and cold differ, as in the same spear, a puncture made by a very sharp point differs from the blow of the rough wooden handle intended for piercing.

To enter into the countless other varieties of tactile qualities is not for this occasion, since most arise from the superficial rather than the central constitution of things; nevertheless we shall touch upon the sources to be explained below (§59). Let us pass on to the extraordinary or physical motions of bodies, which do not arise from gravity or mechanical principles, as far as appears to the senses.